The present invention relates to an optical transmitting system using a heat resistant organic polymer which is superior in transparency, optical members composing of the same, and polymers composing of the same.
A transparent organic polymers such as acrylic resin (simply called polymer hereinafter) is superior in flexibility, and is well known as a substitute for an inorganic glass in order to reduce cost and weight of an optical transmitting system. But, in cases of using as the optical transmitting system for office automation (OA) or for an automobile, no deformation at high temperature such as one hundred and a several tens degrees and no deterioration in capability of optical transmission (transparency) are required, and the required conditions are severer than the transparency and deformation resistance which are required for general organic polymers.
Hitherto, polymethylmethacrylate (PMMA) and polystyrene have been used as materials for substrates composing of the optical transmitting system and for core of optical transmitting portion (plastic optical fiber) which is required superior transparency, but, as thermal deformation temperature of the polymers described above is around 100.degree. C. and heat resistance as an optical fiber is about 80.degree. C., usage of the polymers have been restricted naturally.
In order to improve the restriction, CR-39 (diethylene glycol bis(allylcarbonate)) having thermal deformation temperature of 140.degree. C. as disclosed in JP-A-62-25706 (1987), or bisphenol-A type polycarbonate (PC) having thermal deformation temperature of 130.degree. C. as disclosed in JP-A-57-46204, etc. have been proposed as a material for the core.
Further, a method for improving heat resistance by using cross-linked acrylic polymer is proposed as disclosed in JP-A-57-45502 (1982).
The prior arts described above had a problem that the core of the optical transmitting portion became impossible to transmit light on account of deterioration and strong coloration of the core of the optical transmitting portion after using for thousands hours at 125.degree. C. which was the standard heat resistance temperature of electronic members. The colouration is based mainly on thermal oxidizing deterioration of the polymers. To reduce the colouration, a method to add various stabilizers etc. to the polymer was adopted, but the thermal oxidizing deterioration could not be prevented substantially and there was a problem in usage of the polymer using the stabilizers in the optical transmitting system which required continuous using for long period with high reliability.
Moreover, as the stabilizers became main causes of increment of attenuation loss of the optical fiber, a quantity of addition was required to be less as possible, hence sufficient effect was not brought. And, there was another problem that the core material using cross-linked polymer was poor in productivity.
The prior art, which is incapable of improving the heat resistance without increasing the attenuation loss by introducing a heat resisting structure such as benzene ring etc. which has large light absorption into the molecular structure and by addition of the stabilizers, is a retrogressive art in view of transparency which is the object of the optical polymer for the optical transmitting system.
Accordingly, a method of substituting hydrogen in the molecule with deuterium or fluorine in order to improve transparency of the polymer is considered. But there are problems such as that the deuterium substituted polymer increases moisture absorption, and the fluorine substituted polymer lowers refractive index and makes selection of cladding material difficult.
The object of the present invention is to provide a polymer having superior transparency and heat resistance for optical use and an optical transmitting system using the polymer.